ORA-29279: SMTP permanent error: 501 5.5.4 Invalid Address

Hi Expert,

Recently, I create the new procedure to send email with ("To:" and "Cc" recipient). Then, I run the procedure and display the below of error message. Please help to check my procedure any issue?

ORACLE error 29279 in FDPSTP

Cause: FDPSTP failed due to ORA-29279: SMTP permanent error: 501 5.5.4 Invalid Address

ORA-06512: at "SYS.UTL_SMTP", line 20

ORA-06512: at "SYS.UTL_SMTP", line 98

ORA-06512: at "SYS.UTL_SMTP", line 240

ORA-0651

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create or replace PROCEDURE check_ap_reject_list (errbuf VARCHAR2, retcode NUMBER) IS

  CURSOR c1 IS

  SELECT distinct b.NAME AP_ORG, a.ORG_ID ORG_ID, a.source source,